The present invention relates to a linear actuator drive control apparatus which can carry out precise velocity and positioning control.
Until now, there have been means for utilizing a motor or a linear motor, or means for utilizing fine actuators, such as piezoelectric elements, to accomplish precise linear drive.
FIG. 1 is a summarized cross-sectional view of one example of a means indirectly obtaining a linear driving force utilizing a motor. A rotational driving force obtained by a motor 1 is transferred to a ball screw 5 through pulleys 2 and 3 and a belt 4, converted into the linear driving force by a ball screw nut 6 into which the ball screw 5 is screwed, and linearly drives a driving base 8 through a supporting bracket 7.
FIG. 2 is a summarized cross-sectional view of one example of a means for directly obtaining a linear driving force utilizing a linear motor. A slider 131 of a linear motor 13, having a stator 132, is fixed to a driving base 11 through a supporting bracket 12 and the driving base 11 is linearly driven by the linear driving force of the linear motor 13.
FIG. 3 is a summarized cross-sectional view of one example of a means for directly obtaining a linear driving force utilizing fine actuators such as piezoelectric elements. Both ends of a cylindrical driving fine actuator 21 which can axially expand and contract are respectively fastened to side faces of fixing/separating fine actuators 22 and 23 like the fine actuator 21, and a rod-like driving base 24 is fastened to the side face of the fixing/separating fine actuator 22 so that its longitudinal axis is coincident with the direction of expansion and contraction of the driving fine actuator 21. In the actuator unit of such a structure, the driving base 24 runs through the side of a box-like supporting bracket 25, and the fixing/separating fine actuators 22 and 23 are housed in the supporting bracket 25 so that they support the inside face of the supporting bracket 25 in an expansion state and come apart from the inside face of the supporting bracket 25 in a contraction state.
FIG. 4 is a block diagram of one example of a driving apparatus of the linear driving means shown in FIG. 3. A position controlling circuit 414 inputs a velocity signal VS and outputs expansion/contraction signals SS3, SS4 and SS5 to each of drives 433, 434 and 435. Each driver 433, 434 and 435 supplies each of the expansion/contraction signals SS3, SS4 and SS5 to the respective fine actuators 21, 22 and 23 after power amplifications. An example of each of the expansion/contraction signals and each of the driver's outputs is shown by the time charts of FIGS. 5A-5D, and the velocity signal is in proportion to frequency of each of the expansion/contraction signals. Its operating sequence will be explained referring to the time charts shown in FIGS. 5A-5D as follows.
(1) Time t.sub.o -Time t.sub.1
The driving fine actuator 21 stops in the contraction state and the fixing/separating fine actuator 23 operates from the contraction state to the expansion state, i.e., from the condition that the fine actuator 23 separates from the inside face of the supporting bracket 25 (separating mode) to the condition that it supports the inside face of the supporting bracket 25 (fixing mode), and then the operation of the fixing/separating fine actuator 22 operates from the fixing mode to the separating mode. Therefore, the driving base 24 remains stopped.
(2) Time t.sub.1 -Time t.sub.2
The driving fine actuator 21 operates from the contraction state to the expansion state under the conditions that the fixing/separating fine actuator 23 is in the fixing mode and the fixing/separating fine actuator 22 is in the separating mode. The fixing/separating fine actuator 22 and the driving base 24 fastened by this actuator 22 are driven by these conditions.
(3) Time t.sub.2 -Time t.sub.3
The driving fine actuator 21 stops during the expansion state, and the fixing/separating fine actuator 22 operates from the separating mode to the fixing mode, and then the fixing/separating fine actuator 23 operates from the fixing mode to the separating mode. Therefore, the driving base 24 remains stopped.
(4) Time t.sub.3 -Time t.sub.4
The driving fine actuator 21 operates from the expansion state to the contraction state under the conditions that the fixing/separating fine actuator 22 is in the fixing mode, and the fixing/separating fine actuator 23 is in the separating mode. The fixing/separating fine actuator 23 is driven, and the driving base 24 remains stopped by these conditions.
The above described sequence is one cycle of the operation of the linear driving means utilizing the conventional fine actuators.
In the above described linear driving means utilizing the motor, a mechanical converting mechanism, such as the ball screw, is always required to supply the linear driving force to the driving base 8. Therefore, there are problems in that precise movement cannot be attained because of mechanical strain or looseness of the converting mechanism, and the poorness of the transmission efficiency induced by the mechanical loss of the converting mechanisms. In addition, since the motor utilizes an electromagnetic force, a limitation naturally exists in the compactness because of the large size (the diameter and the length) of the motor is necessary in order to generate the appropriate torque.
In the above described linear driving means utilizing the linear motor, although the mechanical converting mechanism shown in FIG. 2 is not required and it is the compact mechanism, the length of a stator 132 opposite to the slider 131 of the linear motor 13 is required to be the length of one stroke to obtain the driving force over the whole stroke and it must be large because of its driving principle and is therefore expensive.
In the above described linear driving means utilizing the fine actuator, although it is a compact and simple mechanism, smooth movement cannot be obtained because of the intermittence of the movement of the driving base 24 repeatedly starting and stopping.